By Parisa Hafezi, Louis Charbonneau and John Irish LAUSANNE, Switzerland (Reuters) - The United States said on Tuesday that world powers and Iran would keep negotiating over an outline accord on curbing Tehran's nuclear program beyond a midnight deadline, even though tough questions remain. As Iran affirmed its "nuclear rights", the talks in the Swiss city of Lausanne had appeared to be bogged down while officials cautioned that any agreement would probably be fragile and incomplete. "There are several difficult issues still remaining."? For nearly a week, the United States, Britain, France, Germany, Russia and China have been trying to break an impasse in the talks, which are aimed at stopping Iran from gaining the capacity to develop a nuclear bomb in exchange for easing international sanctions that are crippling its economy. A senior Iranian negotiator said Tehran was willing to continue talks until the deadlock is resolved.

Saudi Arabia has been leading a coalition of Arab states since last Thursday in an air campaign against the Shi'ite Houthis, who emerged as the most powerful force in the Arabian Peninsula's poorest country when they seized Yemen's capital last year. The Saudis say their aim is to restore President Abd-Rabbu Mansour Hadi, who left the country last week. The Houthis are allied with Saudi Arabia's regional foe Iran, and backed by army units loyal to longtime ruler Ali Abdullah Saleh, who was pushed out three years ago after "Arab Spring" demonstrations. Residents and tribal sources in north Yemen reported artillery and rocket exchanges along several stretches of the Saudi border.

By Osman Orsal and Humeyra Pamuk ISTANBUL (Reuters) - An Istanbul prosecutor died from his wounds after security forces stormed the office where members of a far-left Turkish group took him hostage on Tuesday, killing his two captors. The Revolutionary People's Liberation Party-Front (DHKP-C) had published a picture of the prosecutor with a gun to his head and said it would kill him unless its demands were met. Turkish President Tayyip Erdogan said Mehmet Selim Kiraz had been shot three times in the head and twice in the body. Six hours after the standoff in a courthouse in central Istanbul began, explosions and gunfire could be heard coming from the building and smoke billowed from a window, a Reuters witness said.

WASHINGTON (Reuters) - U.S. and allied military forces have carried out eight air strikes against Islamic State militants in Iraq and Syria since Monday, according to a U.S. military statement on Tuesday. Bombers, fighters and attack aircraft hit Islamic State targets near several cities, including Mosul and Tikrit in seven strikes during a 24-hour period, it said. One strike in Syria hit targets near the northern border town of Kobani, the statement said. (Reporting by Washington Newsroom; Editing by Sandra Maler)

By Tim Cocks and Alexis Akwagyiram ABUJA (Reuters) - Three decades after seizing power in a military coup, Muhammadu Buhari became the first Nigerian to oust a president through the ballot box, putting him in charge of Africa's biggest economy and one of its most turbulent democracies. As the scale of this weekend's electoral landslide became clear, President Goodluck Jonathan called Buhari on Tuesday to concede defeat to the opposition leader, Buhari's camp said, an unprecedented step that should help to defuse anger among Jonathan's supporters. "Goodluck is a stupid man for conceding, a disappointment for Nigeria," one waitress in the oil city of Port Harcourt said, throwing a beer bottle top at a fridge. Jonathan's People's Democratic Party (PDP) has been in charge since the end of army rule in 1999 but had been losing popularity due to a string of corruption scandals and the rise of Boko Haram's Islamist insurgency in the northeast.

By Victoria Bryan BERLIN (Reuters) - The German pilot who crashed a plane in the French Alps last week, killing 150 people, told officials at a Lufthansa training school in 2009 that he had gone through a period of severe depression, the airline said on Tuesday. The statement is potentially damaging for the airline and its CEO Carsten Spohr, who told reporters last week that the carrier knew of no reason why 27-year-old Andreas Lubitz might deliberately crash a plane. The fact that Lufthansa officials were aware that Lubitz suffered from depression raises questions about its screening process for pilots as it faces the threat of legal action from relatives of the victims. Lufthansa said Lubitz broke off his pilot training for a period of several months but then passed medical checks confirming his fitness to fly.

ZILINA, Slovakia (AP) — Ondrej Duda scored after the interval to lead Slovakia to a 1-0 victory over the Czech Republic on Tuesday in a friendly between the two teams that once represented Czechoslovakia.

Istanbul (AFP) - The Istanbul prosecutor held hostage by two radical leftists at his offices Tuesday died of his wounds sustained after police launched an operation to free him, the hospital announced.

SANAA, Yemen (AP) — Yemeni military officials say Houthi rebels have taken up positions overlooking the strategic Gulf of Aden, raising the risk they could threaten the global shipping route with heavy weapons.

BANGKOK (AP) — Thailand's military-installed prime minister said Tuesday he plans to lift martial law 10 months after staging a coup, but will invoke a special security measure that critics say is more draconian. The development has sparked concern from human rights groups, lawyers, political parties and scholars who say the measure, Article 44 of a junta-imposed interim constitution, gives Prime Minister Prayuth Chan-ocha unchecked authority over all three branches of government.

US President Barack Obama has approved the delivery of a dozen F-16 aircraft to Egypt that had been frozen after a military-led takeover. The White House said Obama told Egyptian President Abdel Fattah al-Sisi by phone on Tuesday that a 2013 freeze would be lifted. The move comes as Egypt plays a key role in the Arab offensive against Iranian-backed Huthi rebels in Yemen and engages in the fight against the Islamic State group in Libya. The decision would help "create a US-Egyptian military assistance relationship that is better positioned to address the security challenges of the 21st century," said National Security Council spokesperson Bernadette Meehan.

BERLIN (AP) — Lufthansa knew six years ago that the co-pilot of the passenger plane that crashed in the French Alps last week had suffered from a "serious depressive episode," the German airline said Tuesday.

At least 62 children have been killed and 30 injured in Yemen over the past week as fighting has escalated, the United Nations children's agency UNICEF said Tuesday. "Children are in desperate need of protection, and all parties to the conflict should do all in their power to keep children safe," said UNICEF's representative for Yemen, Julien Harneis. Fighting has escalated sharply in Yemen after a Saudi-led coalition over the weekend launched air strikes to block an advance by Shiite rebels know as Huthis.

Lawyers for alleged Boston bomber Dzhokhar Tsarnaev quickly wrapped up their defense case on Tuesday as the four-week old trial entered its final stages. Attorneys for Tsarnaev, who faces the death penalty if convicted of the April 2013 Boston Marathon attack that killed three people and wounded 264, called only four witnesses after prosecutors wrapped their case on Monday. "That is all the witnesses that the defense will present," lawyer Tim Watkins informed the court, following the testimony of an FBI fingerprint expert. Under questioning Tuesday, FBI fingerprint expert Elaina Graff acknowledged that only Tamerlan Tsarnaev's fingerprints had been found on many items of evidence including materials used to manufacture bombs.

French President Francois Hollande insisted on a visit to Berlin Tuesday that France would stick to its reform course despite his Socialist party's setback in local elections. Hollande told a joint press conference with German Chancellor Angela Merkel that support for investment as well as social justice by promoting employment would be his main priorities. "The course has been set and will be stuck to," Hollande said.

WASHINGTON (AP) — President Barack Obama on Tuesday released military aid to Egypt that was suspended after the 2013 overthrow of the government, in an effort to boost Cairo's ability to combat the extremist threat in the region.

Nigeria's former military leader Muhammadu Buhari claimed a historic election victory in Africa's most populous country on Tuesday, sending thousands of jubilant supporters into the streets chanting "change, change". Buhari's campaign spokesman said incumbent President Goodluck Jonathan had called the retired general to concede defeat in the most closely fought election in Nigeria's history. If confirmed, this would be the first ever democratic change of power in Nigeria and cap a remarkable comeback for the 72-year-old, who headed a short-lived military regime in the 1980s. Thousands of jubilant Buhari supporters poured into the streets in celebration, many in northern Nigeria which has borne the brunt of the bloody six-year Boko Haram uprising.

Regional rivals Saudi Arabia and Iran traded accusations Tuesday over the escalating conflict in Yemen, which the UN rights chief warned was on the brink of "total collapse". The Huthi rebels and their ally, former president Ali Abdullah Saleh, "decided with the support of Iran to destabilise Yemen," Saudi Foreign Minister Prince Saud al-Faisal said. Tehran hit back, accusing Riyadh of putting the entire Middle East in jeopardy. Iranian state media rejected as "utter lies" claims Tehran had sent arms to Yemen, but said it had dispatched non-military aid, including food and medicine.

Goodluck Jonathan's rise to the top of the pile in Nigeria's ruthless political world has been described as accidental -- a matter of good luck. The 57-year-old southern Christian -- the first head of state from the oil-producing Niger Delta -- was thrust into the presidency in 2010 following the death of his predecessor Umaru Musa Yar'Adua, a Muslim from the north.

Muhammadu Buhari, who has claimed victory in Nigeria's most closely fought presidential election, is not a man who is easily put off. He has been portrayed as a religious zealot and it was claimed that he was ineligible to even stand as he could not initially prove that he had finished his secondary education.

LAUSANNE, Switzerland (AP) — Nuclear talks between Iran and six world powers will pass the negotiators' self-imposed Tuesday night deadline to produce the outline of an agreement and will be extended by at least a day, the United States said.

Major U.S. stock indexes veered lower in late-afternoon trading Tuesday, on course for their first decline in two days. Traders seized on the final day of the quarter to do some profit-taking and prune their portfolios. Health care stocks were among the biggest decliners. Oil prices extended their slide.

China's Communist rulers have turned against the exclusive sport of golf with the government saying nearly 70 "illegal" courses have been closed, seemingly enforcing a decade-old ban for the first time. The announcement by the ministry of land and resources comes amid a high-profile anti-graft campaign spearheaded by President Xi Jinping, which has seen crackdowns on banquets, lavish gift-giving and other official excesses. The ruling Communist Party has long had an ambivalent relationship with golf, which is a lucrative opportunity for local authorities and a favoured pastime of some officials, but is also closely associated with wealth and Western elites. "Presently, local governments have shut down a number of illegally-built golf courses, and preliminary results have been achieved in clean-up and rectification work," read the announcement on the ministry's website late Monday.

Exiled former Malian leader Amadou Toumani Toure has given evidence in a probe into alleged Libyan funding for Nicolas Sarkozy's 2007 French presidential election campaign, an aide said Tuesday. He was "asked what he knows of Libyan financing" allegedly provided to Sarkozy by former dictator Moamer Kadhafi, the source told AFP, adding that Toure would not face further questioning. Local media said Toure spoke to investigators on March 24, but Senegal's criminal investigations division refused to comment. Amadou Cheikh Bani Kante, former special adviser to Toure on Libyan investments in west Africa, has been implicated in the case as a possible "bag carrier" -- or go-between -- for the Kadhafi regime.

Iraq said security and allied forces backed by US-led coalition aircraft "liberated" the city of Tikrit on Tuesday, its biggest victory yet in the fight against Islamic State jihadists. The operation to retake the hometown of former president Saddam Hussein began on March 2 and had looked bogged down before Iraqi forces made rapid advances in the past 48 hours. Prime Minister Haider al-Abadi "announces the liberation of Tikrit and congratulates Iraqi security forces and popular volunteers on the historic milestone," his official Twitter account said. He was referring to paramilitary groups which played a major role in the fighting to retake Tikrit, a Sunni Arab city which IS had controlled since it captured swathes of Iraq in June.

Thousands of people spilled onto the streets of Nigeria in celebration on Tuesday after opposition candidate Muhammadu Buhari claimed victory in the presidential election. A cavalcade of motorbikes and cars with their headlights on and horns blaring paraded through the streets of Kano, northern Nigeria's biggest city, where the retired general won a landslide victory. Drivers performed stunts, filling the air with thick smoke, as veiled women and the crowds shouted "Sai Buhari" (Only Buhari) in celebration. Kano is among the Nigerian states hit hardest by Boko Haram Islamists, where many have criticised President Goodluck Jonathan's handling of the insurgency.

The Council of Europe on Tuesday blasted Kiev for failing to properly investigate deadly violence against demonstrators in last year's Maidan protests that ended with pro-Russian president Viktor Yanukovych's downfall. The council reviewed records detailing violence in Kiev's Independence Square, or Maidan -- the focal point of the pro-European protests -- from November 2013 to February 2014. Rights groups have frequently accused Ukraine's current leaders of failing to bring to justice those responsible for the Maidan violence, in particular a three-day bloodbath in February. Dozens of demonstrators who set up camp on the square also disappeared and are still missing.

Libyan antiquities officials looked on with horror at Internet video footage that showed Islamist extremists wielding sledgehammers and power tools to grind ancient Iraqi treasures into dust. They fear the Islamic State group jihadist movement's growing influence means the fate that befell these priceless Assyrian and Akkadian artefacts now awaits their own rich heritage dating back millennia. Footage of the cultural atrocity showed militants smashing exhibits at the museum in Mosul, Iraq's second city and the main IS stronghold since its capture in a lighting June offensive last year. Libya, another country rich in archaeological heritage, has been in turmoil since the 2011 overthrow of longtime dictator Moamer Kadhafi in a NATO-backed uprising.

TIKRIT, Iraq (AP) — Iraqi forces battled Islamic State militants holed up in downtown Tikrit, going house to house Tuesday in search of snipers and booby traps, and the prime minister said security forces had reached the heart of the city.